1. Field of the Invention
The present invention relates to a dust removal system for a riding lawn mower, comprising an engine disposed within an engine compartment partitioned by a separating wall, a speed change device disposed outside of the engine compartment, and a universal coupling inserted through an opening provided in the separating wall in order to connect an output shaft of the engine with an input shaft of the speed change device.
2. Description of the Related Art
One example of a conventional dust removal system for a riding lawn mower comprises a universal coupling which fits in an open edge of a draft guide cover for covering a cooling fan from the front, with the cooling fan rotating integrally with an output shaft of an engine; and a perforated board which rotates integrally with the universal coupling, wherein grass cuttings are prevented by the perforated board from flowing into an engine compartment through the opening in the draft guide cover. This example is known from JP (Kokai) No. 2005-287341. The universal coupling is composed of a first connecting shaft connected to the output shaft of the engine, an intermediate shaft, and a second connecting shaft fitted by splines with an input shaft of a transmission mechanism; and is configured so that the shafts are all bendably connected, and the perforated board rotates integrally with the intermediate shaft of the universal coupling. The draft guide cover is provided so as to cover the cooling fan from the front, with the cooling fan rotating integrally with the output shaft of the engine.
In the conventional dust removal system described above, when the universal coupling bendably deforms due to the vibration of the engine or another such cause, the perforated board is swingably displaced relative to the draft guide cover about the connecting part between the first connecting shaft and the intermediate shaft in the universal coupling. When the space between the perforated board and the draft guide cover is therefore enlarged in order to avoid interference between the perforated board and the draft guide cover due to the swinging displacement, there is a greater possibility that grass cuttings or other such small debris will flow with outside air into the engine compartment through the space between the perforated board and the draft guide cover. As a result, grass cuttings and other such small debris adhere to and accumulate in the periphery of the engine and other such locations, increasing the danger of overheating as a result of impeding the flow of outside air. When the space between the perforated board and the draft guide cover is made smaller in order to avoid such occurrences, the perforated board readily interferes with the draft guide cover, and there is a danger that this interference will cause unusual sounds or damage to the perforated board or draft guide cover.
In view of this, it has been proposed that by configuring the perforated board to rotate both around and integrally with the output shaft of the engine, the perforated board will not be swingably displaced even if the universal coupling bendably deforms due to the vibration of the engine or other such causes. The intention is to thereby forestall the occurrence of unusual sounds and damage to the perforated board or draft guide cover due to interference between the perforated board and draft guide cover resulting from the swinging displacement of the perforated board, without enlarging the space between the perforated board and the draft guide cover. However, in this configuration, when the universal coupling bendably deforms due to the vibration of the engine or another such cause, the intermediate shaft of the universal coupling inserted through an insertion hole in the perforated board is swingably displaced relative to the perforated board about the connecting part with the first connecting shaft. Therefore, the insertion hole in the perforated board must be formed large in diameter so as to ensure a space between the perforated board and the intermediate shaft in order to avoid interference between the perforated board and the intermediate shaft as a result of the swinging displacement of the intermediate shaft. However, the circumference of the space secured between the perforated board and the intermediate shaft in this arrangement is much shorter than the circumference of the space formed between the perforated board and the draft guide cover. As a result, there is less of a possibility that grass cuttings or other such small debris will flow with outside air into the engine compartment through the space, in comparison with cases in which a space for avoiding interference between the perforated board and draft guide cover is formed therebetween. However, despite either of the circumferences being small, grass cuttings or other such small debris will flow with outside air through the space between the perforated board and the intermediate shaft, and there is therefore a possibility that the grass cuttings and other such small debris that have flowed in will adhere to and accumulate in the periphery of the engine and other such locations, impeding the flow of outside air in the engine compartment. In other words, there is room for improvement in terms of more effectively suppressing overheating caused by grass cuttings or other such small debris adhering to and accumulating in the engine compartment interior.